Bone rigging incorrectly
EDIT: It turns out you have the Auto IK option enabled. To turn that off, press N with your mouse in the 3d view to open up the sidebar and go to the tools tab.



Uncheck that and you are good to go!

EDIT: The information below did not answer the question directly, but may help others as it can cause a very similar issue.

I looks like you just need to adjust the Chain Length in the IK constraint, found here:



What this does is tell Blender how many bones in the chain to use. The default is 0, meaning the whole chain is used, in your case up to the pelvis. I think you would need to set yours to 3, but you'll be able to see the line update as you change the length.